Lithium soaps are the most common thickeners used in the formulation of lubricating greases. Lithium soaps used for grease making are classified into two types: simple soap and complex soap. The main performance difference between the two is the greater thermal stability of the lithium complex greases as seen in the dropping point (ASTM D566 or D2265). Both types contain the lithium salt of a fatty acid. Lithium complex soaps contain an additional lithium salt, or “complexing agent”, most commonly a dilithium salt of a low molecular weight dibasic organic acid or dibasic ester.
Lithium greases can be manufactured by continuous process in a heated tube reactor (U.S. Pat. Nos. 4,297,227; 3,475,335; and 4,444,669). The process is most convenient and problem-free for simple lithium soap thickened greases. However, lithium complex greases having much higher thickener concentrations resulted in increased difficulties during continuous production. These difficulties include wide fluctuations in flow rates, cessation of flow and resultant downtime, and greatly reduced unit production capacity.